Polyurethane-forming compositions are widely used in a variety of commercial, industrial and household applications, such as in automotive clear-coat and seat cushion applications. Polyurethane systems that employ isocyanates which are pre-reacted with monofunctional reagents to form relatively thermally labile compounds are called blocked isocyanates. Uretdiones are a type of blocked isocyanate. Uretdiones are typically prepared by dimerizing an isocyanate to form uretdione(s) with unreacted isocyanate end-groups which can then be extended with a polyol to form a polymeric material containing two or more uretdione groups in the polymer chain. In some literature, uretdiones are referred to as “1,3-diaza-2,4-cyclobutanones”, “1,3-diazatidin-2,4-diones”, “2,4-dioxo-1,3-diazetidines”, “urethdiones” or “uretidiones”. Typically, the polymer has few, if any, free isocyanate groups, which is achieved by controlling the stoichiometry of the polyisocyanate, of the polyol, and by the use of a blocking agent.
The reaction of uretdiones with polyols to form polyurethane coatings is well known in the art, especially in polyurethane powder coatings. However, the creation of allophanates from uretdiones and polyols at ambient or low temperatures in the presence of a tertiary amine catalyst has not been well-studied in the literature. To the best of the present inventors' knowledge, no one has developed a cross-linking approach using neutralized polyols to promote successful conversion of uretdione to allophanate at ambient or low temperatures in the presence of tertiary amine catalysts over neutralized basecoats.